i noticed on the rebelscum photo archives that the grey arc trooper from the regular CW line had two versions, one w/grey sholder pad and one w/blue shoulder pad. was the one with the grey pad just released in the bonus 2-pack or is there one that was also released on a regular single card like the blue pad version?

The grey pad was released in the 2-packs, but also on the earlier single cards. Then the running change was made shortly thereafter to the newer, more accurate blueish color. But it's not an "intentional" paint variation like we're probably going to get on the new Red ARC Trooper, which will probably be made in a blue version later on.

They just realized the paint color was wrong and made some revisions to it. Those earlier grey ones are rather ugly though, as the shoulder articulation point didn't get painted at all (stayed white), so there's a white stripe right in the middle of the grey pad. Bad.